1. Field of the Invention
This invention relates to an adjustable, pinch-off neck assembly for a container blow mold system. The assembly of the present invention facilitates lateral positioning of the pinch off neck assembly so as to reduce pinch-off separation and increase the effectiveness of the pinch-off.
2. Description of the Prior Art
The extrusion blow molding of plastic containers is well known and offers may advantages over other forms of container manufacturing. Among these advantages are the ability to produce containers with low start-up costs; to produce containers at a minimal per container cost; to produce containers with a minimal amount of material waste; to produce containers with irregular shapes; and to produce containers from a variety of materials, with the selected material having qualities particularly suited to the given application.
Molds for producing such extrusion blown containers are commonly made with each half of the mold including a main mold portion and a top block or pinch-off neck assembly. The main mold includes surfaces defining a cavity bearing the shape of one half of the container body. A neck finish cavity is defined by surfaces in the pinch-off neck assembly. Since a variety of neck finishes may be used on common container body styles (for example, the neck finish may be threaded for use with a threaded closure or it may be non-threaded and adapted for mating with a snap-on enclosure), the main mold interchangeably accepts the pinch-off neck assemblies. Pinch-off neck assemblies are themselves provided in halves and are typically bolted to the top of the main mold halves. In mounting the pinch-off neck assembly halves to the main mold halves, the parting face on each pinch-off neck assembly half is precisely aligned with the corresponding parting face of its respective main mold half.
During extrusion blow molding, molten plastic is extruded in the form of a hollow tube or parison and positioned between the open mold halves. The mold halves close trapping the parison within the mold cavity. When closed, the various parting faces of the mold are mated with one another. In the pinch-off neck assembly, the parting face are generally raised one to two thousandths of an inch so as to "pinch-off" the parison material in that area. The result is that no flash is formed in the neck finish area. This is desirable because of the cost that would be involved in trimming flash from such a detailed area of the container and because of the desired detail in the neck finish area. A blow pin assembly is then lowered, forcibly engaging the uppermost portion of the neck opening in the pinch-off neck assembly. A blow pin enters into the parison and a gas blowing medium, provided through the blow pin, inflates the parison causing it to conform to the shape of the mold cavity.
The blow pin assembly exerts a significant force during blow molding. This force is often great enough to cause separation of the parting faces in the pinch-off neck assembly. With the neck finish often being the most detailed feature of the container and requiring the highest degree of accuracy in its formation, it is important to prevent separation of the pinch-off neck assembly to the degree where the effectiveness of the pinch-off assembly is diminished, flash is formed and the subsequent closure cap will not properly fit with the neck to seal the container opening.
Previously, to fine tune positioning of the pinch-off neck assembly, bolts securing the pinch-off neck assembly to the main mold halves were loosened and the pinch-off neck assembly shimmed in a trial and error method until the proper amount was achieved to prevent separation. Such an adjustment technique is extremely cumbersome and time consuming.
Accordingly, it is an object of the present invention to provide an improved pinch-off neck assembly.
It is also an object of this invention to provide a pinch-off neck assembly which is axially adjustable.
A further object of this invention is to provide a pinch-off neck assembly where individual assemblies can be adjusted while remaining mounted to the a mold half.